Loud-speaker condenser



p 6, 1930. P. E. EDELMAN 1,776,112

LOUD SPEAKER CONDENSER Filed April 8, 1929 2 Shuts-Shoot 1 x 7L I v; 2

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GHICAQO, ILLINOIS LOUD-SPEAKER CONDENSER Applicationflled April 8, 1929. Serial No. 353,562.

My present invention relates to condenser reproducers and improvements in a loud.

Heretofore, a limitation to the use of condenser type reproducers has been imposed by 1 relatively poor volume response thereof in comparison with 'electrodynamic type reproducers. I have conceived and proved that, this problem of securin greater volume of response canv be solve by improved and novel structure for the speaker d aphragms. I illustrate, by way of example, a suitable embodiment of my invention which I have constructed and satisfactorily tested.

Reference is made to the accompanying drawings, in which- Figure 1 is a rear view elevation of the con-- denser assembly;

Fig. 2 is a sectional view or a part of the condenser assembl' showing the relation of 26 the plurality of diaphragm elements used;

and

Fig. 3 shows a modified construction similar to Fig. 2 with the addition. theretoof a vibration controlling fabric.

In other applications for Letters Patent of the United States, I have disclosed the prefcrred'circuits for operating a condenser speaker of this type. My present invention is characterized by a condenser structure in which a dielectric diaphragm, such as empire cloth, stretched over a supporting frame and carrying a conductive electrode coating, is placed closely adjacent not only to one co-opcratingflexible porous electrode as heretofore practiced, but to a plurality of adjacently disposed and freely mounted metallic perforated ribbons, each of which serves as an electrode and sound reproducer, thereby greatly multiplying the volume of response of the condenser speaker for a given input excitation energy therefor.

In Fig. 1, the expans'ible frame 1 may be expanded by means of corner wedges 2 and carries a soft rubber fabric gasket 8 over as which the condenser diaphragms i and 5 are stretched. Each ribbon electrode 5 mounted back of. dielectric dia hragm 4, for example, consists preferably 0 a perforated ribbon of soft zinc or lead foil about .02" thick, containing a multiplicity of perforated holes 6'of about diameter disposed inch apart in the width of strip 5, and fij'apart in the length of metal strip 5. Each adj acently disposed strip 5 is separated from the next strip by an air gap 17 of about inch, so as to be free to flex, twist and stretch independently of the next adjacent strips 5.

A cross connector ribbon of metal 7 interconnects the strips 5 electrically for parallel electrical operation thereof, permittin independent mechanical performance o. each strip 5. Atwistin action of stri s 5, not possible if air gap 1 were omitt is thereby attained, affording a far greater volume of response than heretofore considered ossible in this art. In stretching strips 5 on rame 1, each strip 5 also becomes slightly contoured or curved onone surface, facilitatin the aforesaid crosswise twisting action com ined with-lengthwise flexing under the influence of electrical stresses applied thereto in. use. The strips 5 are overlapped on one end of frame 1 at 8 to facilitate electrical connection through the connector strip 7 to termical 12.

The strips 5 must be made of'relatively soft metal, such as zinc or lead, which are substantially nonelastic and which hence add no artificial resonance to the reproduced sound. The order of sound. reproduction thereby attained in comparison to the best previously known constructions for the flexible electrode connected by terminal 12 is at least 400 per cent greater for a given input energy to the condenser carried on frame 1 with full brilliancy of reproduction, includingall tones and overtones within the range of audible frequencies.

A suitable size for frame 1 is 16" by 30", though any other desired size may be used, larger or smaller than this. As shown, in Fig. 2, diaphragms 5, as well as dielectric diaphragm 4;, are fastened to frame 1 by tacks l3. The ribbon diaphragms 5 are'first stretched over frame 1, after wlziich a dielectric diaphragm 4: made, for example, of empire cloth .005" thick, or varnished fabric impregnated with oxidized linseed oil, is stretched thereovcr. The frame 1 is expanded to draw member l and members 5 closely adjacent, but separated by a thin air gap or space 8 which maybe of very minute dimensions.

Perforations 6 in the metal strips 5 permil; the free flow of air from the air gap 8 through the flexible electrode diaphragms 5. The dielectric diaphragm i is coated with japan varnish size 9 on the top side thereof, and carries a thin covering or electrode 10 of metal foil, such as aluminum foil .0002 inch thick. A tinsel or flexible metal strip connector 11 is fastened to the electrode 10 carried by the diaphragm l. A connector terminal 12 is fastened to all of the adjacently disposed diaphragm ribbons 5. Frame 1 has a projecting portion 14 to insure that diaphragms l and 5 will be drawn closely together when frame 1 is expanded by means of wedges, shown in Fig. 1. The gasket 3 of soft rubber fabric tends to hold the diaphragzns i and 5 taut during use thereof.

In Fig. 3 is shown a reversed modified assembly for ti elements of Fig. 2, with the addition of a dampening fabric covering 16 in lieu of gasket 3 of Fig. 2. This fabric covering 16 is stretched over flexible electrode strips 5 and made of a stretchable textile fabric of porous characteristics, such as monk cloth or crash.

in Fig. 3 the dielectric diaphragm at with its electrode coating it) is first stretched over frame 1, and held by tacks l3 thereon. Next the perforated metal ribbons 5 are stretched over diaphragm 4t, and fastened to frame 1 by tacks 13. Then vibration controlling fabric 16 is tacked to frame 1 over electrode diaphragins 5. Terminal 12 is fastened to the extending portion 8 of strips 5 by a tech 13. Connector terminals 11 of flexible metallic ribbon is secured to electrode 10 at 15, and attached to wood frame 1 by tack 13.

This assembly has the advantage of limiting the amplitude of response of ribbon electrode diaphragms 5 on very large electro-- static energy input thereto to prevent generation of undesired stationary waves, thereby under the influence of powerful excitation. This modified assembly also affords protection for the delicate foil electrode 10, as the frame 1 projects beyond the surface of the covering 10. A muslin fabric screen 17 may be tacked over frame 1 to assist this aforesaid mechanical protection feature if desired.

While I have shown and described but a few embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims.

1 claim:

1. An acoustic condenser comprising, in combination, a stretched dielectric diaphrag'm, an electrode coating attached on one surface thereof, and a plurality of cooperating flexible electrode strips spaced from each other and mounted adjacent to said dielectric diaphragm.

2. An acoustic condenser comprising, in combination, a flexible electrode impermeable to air llow, a dielectric diaphragm carrying said electrode, and a plurality of parallel electrically connected freely separated flexible metallic ribbon electrodes mounted closely adjacent to said dielectric diaphragm.

3. An acoustic condenser comprising, in combination, a sheet of stretched fabric impregnated with'an insulating compound and coated on one surface with an adhesive varnish, a thin layer of metal foil carried on said varnish coating, and a plurality of cooperating independently spaced perforated soft metal ribbon electrodes disposed closely adjacent to the surface of said impregnated fabric which is not coated with adhesive varnish.

4. An acoustic condenser comprising, in combination, an expansible frame. a plurality of perforated flexible metal ribbons stretched thereover, a dielectric diaphragm stretched over said ribbons and supported by said frame, and a metallic coating on said dielectrio diaphragm.

5. An acoustic condenser comprising, in combination, a frame, a soft yielding gasket thereon, a plurality of thin flexible perforated metal ribbons independently mounted over said gasket and held on said frame, an impregnated fabric diaphragm. stretched adjacent to said metal ribbons, and a co-operat- Ling electrode coating carried on said fabric diaphragm.

6. An acoustic condenser comprising, in combination, a supporting frame, a dielectric diaphragm stretched thereover and fastened thereto, an electrode coating carried by said diaphragm, a plurality of independently mounted perforated electrode metal ribbons stretched closely over said diaphragm with very small air gaps between said ribbons and said diaphragm, and means to control the amplitude of vibration of said ribbons.

i. .An acoustic condenser comprising, in combination, a frame, a diaphragm carried thereby, an electrode on said diaphragm, a plurality of independently spaced perforated soft metal ribbons mounted closely over said diaphragm and separated therefrom by a thin layer of air, and a sheet of porous fabric stretched adjacent and in contact with said metal ribbons to control the amplitude of vibrations thereof.

8. An acoustic condenser comprising, in combination, a frame, a dielectric diaphragm stretched thereon, an electrode coating carried on said diaphragm, a plurality of perforated soft metal flexible riloioons stretched closely near to taid diaphragm and mounted independently item each other of said ribbons on said frame, and a co-operating fabric covering carried. on said frame to limit the amplitude of response of said ribbons when same are connected to a source of electrical excitation in electrical circuit with the eiec trode coating on said diaphragm.

9. An acoustic condenser comprising a mounting frame carrying protecting fabric screens at the "front and back side of said frame, and an electrostaticcondenser repreducei' mounted on said "frame, characterized by the fact that one of said fabric screens is stretcit-eti substantially in contact "with said elleetnostatie condense? re "reducer to control the amplitude of vibiation response thereof.

10. In an acoustic condenser, a dielectric diaphragm, an electrode coating carried thereby, and a plurality of independently mounted (Bo-operating perforated electrodes placed with respect thereto free to twice as weii as flex under the action of eieetricei excitation.

3e testimony whereof i have hereunto set my hand this th day of April 192%.

PHILIP E. EDELMAN 

